in which case a Triangulation object will be created. See
Triangulation for a explanation of these
possibilities.

The next argument must be C, the array of color values, either
one per point in the triangulation if color values are defined at
points, or one per triangle in the triangulation if color values
are defined at triangles. If there are the same number of points
and triangles in the triangulation it is assumed that color
values are defined at points; to force the use of color values at
triangles use the kwarg facecolors=C instead of just C.

shading may be ‘flat’ (the default) or ‘gouraud’. If shading
is ‘flat’ and C values are defined at points, the color values
used for each triangle are from the mean C of the triangle’s
three points. If shading is ‘gouraud’ then color values must be
defined at points.